Conventional wisdom tells us that we should get at least eight hours of sleep a night, but a recent report by the BBC suggests that this might just be a myth.

Historian Roger Ekirch believes that in the past, it was normal to get two sleep sessions, one early evening, a break, and then a second later at night.

The report cites historical evidence that seems to prove this pattern; neighbors visited between sleeps and doctors advised that conception of a child is best between sleep sessions.

Learn more about the report in the video above.

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What Happens During Sleep

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You spend the day awake, alert and burning your body's fuel. Lots of the brain's centers are firing at once to make sense of the visual, auditory and other stimulants happening all around you, says Dr. Epstein. If you were to map out the brain's activity, you'd see "chaotic, small waves" he says. "You can think of it as 'awake brain, awake body.'"
But the body is preparing for sleep long before your head actually hits the pillow, explains Twery. The darker light of evening triggers sleep hormone melatonin to rise, and the body's temperature drops slightly. "These are all signals to the body to promote sleepiness and the transition to sleep," he says.
Flickr photo by D'Arcy Norman

Stages one through three are all what's considered non-rapid eye movement sleep, or NREM. (In the past, NREM sleep was divided into four stages, but stages three and four were consolidated into one in 2007, according to Dr. Epstein.)
The first phase of sleep is a transitional period between wakefulness and sleep, and, as such, is very light sleep. If you're woken up in this early phase of sleep, you most likely won't feel like you've slept at all, reports WebMD.
It typically takes from 90 to 110 minutes to complete one cycle through all the stages of sleep, says Dr. Epstein, and over the course of the night, ideally you'll cycle through them four to five times, says Twery. "When you short-circuit this process -- so, instead of sleeping seven to eight hours a night you sleep fewer hours -- you don't get the full pattern. The body attempts to make due with what it's got, but it's not working efficiently," he says.
While you won't see the effects of cutting your sleep short immediately, he cautions -- "It's not like you stay up late and you have a heart attack" -- over time, a lack of sleep can erode your general health, similarly to the way eating a poor diet and not getting enough exercise can hurt.
Typically, this phase accounts for only five to 10 minutes per cycle, according to WebMD, or about 10 percent of your night, says Dr. Epstein.
Flickr photo by Perfecto Insecto

In this stage, your heart rate and breathing become regular and your body temperature drops. Sleeping in a cool room is helpful because it can get you to that lower temp more quickly, according to the National Sleep Foundation.
While it's deeper sleep than Stage 1, Stage 2 sleep is still light sleep. It's easier to wake someone up from this phase than deeper sleep, and it's also less refreshing, even though it is beginning to become restorative sleep.
You spend about half of the night in Stage 2 sleep, according to the NHLBI, and stay there for longer periods of time as the night goes on, says Dr. Epstein. "It seems to be the default sleep, since you spend so much time in it as you're moving in between these different [stages]," he says.
Flickr photo by Betsssssy

Stage 3 sleep is deep, restorative sleep. Your breathing will slow and your blood pressure will drop. Muscles relax as the blood supply to them increases, promoting growth and repair.
"A good way to describe it is 'asleep brain, asleep body,'" says Dr. Epstein. In contrast to the chaotic brain waves seen during wakefulness, here, the brain is turning itself off, resulting in large, slow waves, he explains.
During this phase, your energy becomes recharged. The body also releases important hormones during Stage 3 sleep, like growth hormone, which is essential to healthy development, says Twery.
When you're tired, it's this deep sleep that your body is craving, explains Dr. Epstein, so you'll move more quickly through Stages 1 and 2 and spend a larger amount of time in Stage 3 early in the night. Eventually, time spent in this stage peters out; overall, you spend about 20 percent of the night here.
Flickr photo by Leah Love

Rapid eye movement or REM sleep first occurs about 90 minutes after falling asleep, and then about every 90 minutes after that. The first time, it may last about 10 minutes, but as the night goes on, REM periods lengthen to as long as an hour, according to WebMD.
The brain is active in REM sleep, which is what allows us to dream. In this stage, "the brain looks like it does when it's awake," says Dr. Epstein. "If you're having a dream about catching the bus to go to work, the part of the brain that makes the legs run is firing, the worry part -- 'Am I going to make the bus?' -- is firing, but you can't actually act out your dreams," he explains. Our muscles are paralyzed in REM sleep so we don't actually run for the bus, so he likes to think of this stage as "awake brain, asleep body."
Woken too quickly during this phase, some people might experience sleep paralysis, when they feel awake and alert but the muscles are still unable to move, explains Twery. You may also feel groggier if you are woken up during REM sleep, he says, which is why napping longer than 20 to 30 minutes isn't a good idea. "If you're forced to wake up after an hour or so, being aroused from sleep may come with some sleep inertia, which may take some time to shake."
REM sleep seems to be most greatly associated to the learning and memory functions of sleep, according to Dr. Epstein -- dreaming may play a role in sorting out which memories from the day are worth keeping, for example. (Remembering your dreams, however, is probably only linked to when you wake up in relation to the dreams, as the memory of dreams only lasts a short time, he explains.)
Also during REM sleep, which accounts for 20 percent of your night, breathing becomes irregular and shallow, according to the NHLBI, and heart rate and blood pressure increase.
Flickr photo by Casey David